Flexible polyurethane foams

ABSTRACT

Process for preparing a flexible polyurethane foam by reacting a polyisocyanate and two different polyols under foam forming conditions so as to prepare a rigid foam and by crushing the rigid foam so obtained. Flexible foams are obtained which do not show a major glass transition temperature between -100° C. and +25° C.

This application is a Divisional of U.S. application Ser. No. 09/197,978filed Nov. 23, 1998 which is now U.S. Pat. No. 6,335,379, which is aDivisional of U.S. application Ser. No. 08/641,122 filed Apr. 30, 1996which is now U.S. Pat. No. 5,900,442, which is a continuation-in-part ofU.S. application Ser. No. 08/481,725 filed Jun. 7, 1995 abandoned.

The present invention is concerned with flexible polyurethane foams anda process to prepare such flexible polyurethane foams.

Flexible polyurethane foams are widely known. Such foams show arelatively high resilience (ball rebound), a relatively low modulus, arelatively high sag factor and a relatively low hysteresis loss.

Such foams further show a major glass-rubber transition below ambienttemperature, generally in the temperature range of −100° C. to −10° C.The commonly applied relatively high molecular weight polyether andpolyester polyols in such foams are responsible for the sub-ambientglass transition temperature (Tg^(s)). These polyether and polyesterpolyols are often referred to as soft segments. Above Tg^(s) the foamdisplays its typical flexible properties until softening and/or meltingof the isocyanate-derived urethane/urea clusters (“hard domains”) takesplace. This softening and/or melting temperature (Tg^(h) and/or Tm^(h))often coincides with the onset of thermal degradation of polymersegments. The Tg^(h) and/or Tm^(h) for flexible polyurethane foams isgenerally higher than 100° C., often even exceeding 200° C. At theTg^(s) a sharp decrease of the modulus of the flexible foam is observed.Between Tg^(s) and Tg^(h)/Tm^(h) the modulus remains fairly constantwith increasing temperature and at Tg^(h)/Tm^(h) again a substantialdecrease of the modulus takes place. A way of expressing the presence ofTg^(s) is to determine the ratio of the Young's storage modulus E′ at−100° C. and +25° C. as per Dynamic Mechanical Thermal Analysis (DMTAmeasured according to ISO/DIS 6721-5). For conventional flexiblepolyurethane foams the$\frac{E^{\prime} - {100{^\circ}\quad {C.}}}{E^{\prime} + {25{^\circ}\quad {C.}}}\quad \text{ratio is at least 25.}$

Another feature of Tg^(s) by DMTA (ISO/DIS 6721-5) is that forconventional flexible polyurethane foams the maximum value of the$\text{ratio of}\quad \frac{\text{Young's loss modulus}E^{''}}{\text{Young's storage modulus}E^{\prime}}\quad \left( {\tan \quad \delta_{\max.}} \right)\quad {over}\quad {the}$

−100° C./+25° C. temperature range varies from 0.20-0.80 in general. TheYoung's loss modulus E″ is measured by DMTA (ISO/DIS 6721-5) as well.

In the context of the present application a polyurethane foam isregarded as flexible when the ball rebound (measured according to ISO8307 with the proviso that no preflex conditioning is applied, that onlyone rebound value per sample is measured and that test pieces areconditioned at 23° C.±2° C., (50±5% relative humidity) is at least 40%,preferably at least 50% and most preferably 55-85% in at least one ofthe three dimensional directions. If in the present application ISO 8307is mentioned it refers to the test as described above including theprovisos. Preferably such flexible foams have a Young's storage modulusat 25° C. of at most 500 kPa, more preferably at most 350 kPa and mostpreferably between 10 and 200 kPa (Young's storage modulus measured byDMTA according to ISO/DIS 6721-5). Further, such flexible foamspreferably have a sag factor (CLD 65/25) of at least 2.0, morepreferably at least 3.5 and most preferably 4.5-10 (measured accordingto ISO 3386/1). Still further such flexible foams preferably have a CLDhysteresis loss (ISO 3386/1) of below 55%, more preferably below 50% andmost preferably below 45%.

In the context of the present patent application polyurethane foams areconsidered as rigid if the ball rebound is below 40%, as measuredaccording to ISO 8307, at a free rise core density of the foam of 3-27kg/m³.

Preferably the ratio E′_(−100° C.)/E′_(+25° C.) of such a rigid foam is1.3-15. Conventional flexible foams are made by reacting apolyisocyanate and a relatively high molecular weight isocyariatereactive polymer, often a polyester or polyether polyol, in the presenceof a blowing agent and optionally further using limited amounts ofrelatively low molecular weight chain extenders and cross-linkers andoptionally using additives like catalysts, surfactants, fire retardants,stabilisers and antioxidants. The relatively high molecular weightisocyanate reactive polymer in general represents the highest weightfraction of the foam. Such flexible foams may be prepared according tothe one-shot, the quasi- or semi-prepolymer or the prepolymer process.Such flexible foams may be moulded foams or slabstock foams and may beused as cushioning material in furniture and automotive seating and inmattresses, as carpet backing, as hydrophilic foam in diapers and aspackaging foam. Further they may be used for acoustic applications, e.g.sound insulation. Examples of prior art for these conventional flexiblefoams are EP-10850, EP-22617, BP-111121, EP-296449, EP-309217,EP-309218, EP-392788 and EP-442631.

Conventional rigid foams are made in a similar way with the proviso thatoften the polyisocyanates have a higher isocyanate functionality, theamount of high molecular weight polyols used is lower and the amount andfunctionality of the cross-linkers is higher.

WO92/12197 discloses an energy-absorbing, open-celled, water-blown,rigid polyurethane foam obtained by reacting a polyurethane foamformulation, comprising water which acts as a blowing agent and acell-opener, in a mould wherein the cured foam has a moulded density ofabout 32 to 72 kg/m³ and a crush strength which remains constant from 10to 70% deflection at loads of less than 70 psi. The foams have minimalspring back or hysteresis.

GB2096616 discloses a directionally flexibilized, rigid, closed-cellplastic foam. The rigid foams are flexibilized in order to use them fore.g. pipe-insulation. Cells should remain closed.

U.S. Pat. No. 4,299,883 discloses a sound-absorbent material made bycompressing a foam having closed cells to such an extent that the foamrecovers to 50-66% of its original thickness. By the compression thecells are ruptured and the foam becomes flexible and resilient; it mayreplace felt. The disclosure mainly refers to polycarbodiimide foams.

EP561216 discloses the preparation of foam boards having improved heatinsulation properties, wherein the foam has anisotropic cells having alength ratio of the long and the small axis of 1.2-1.6 and a density of15-45 kg/m³ and wherein the cells have been crushed in the direction ofthe plate thickness. The disclosure actually refers to polystyreneboards. Since the disclosure refers to foams having improvedheat-insulation properties, the foams actually have closed cells.

EP641635 discloses a process for preparing foam boards, having a dynamicstiffness of at most 10 MN/m³, by crushing a board of 17-30 kg/m³density at least twice to 60-90% of its original thickness. Preferablyclosed-celled polystyrene is used. In the examples it is shown that apolystyrene foam which has been crushed showed a better heat insulationthan an uncrushed one.

U.S. Pat. No. 4,454,248 discloses a process for preparing a rigidpolyurethane foam wherein a partially cured rigid foam is softened, thencrushed and re-expanded and fully cured.

Surprisingly a completely new class of flexible polyurethane foams wasfound such foams having no major glass-rubber transition between −100°C. and +25° C. In more quantitative terms these foams show a ratioE′_(−100° C.)/E′_(+25° C.) of 1.3 to 15.0, preferably of 1.5 to 10 andmost preferably of 1.5 to 7.5. The tan δ_(max) over the −100° C. to +25°C. temperature range is below 0.2.

The free rise core density of such foams may range from 4-30 kg/m³ andpreferably ranges from 4-20 kg/m³ (measured according to ISO/DIS845).Preferably the foams according to the present invention have a majorglass transition above 50° C. and most preferably above 80° C.

The flexible polyurethane foams according to the present invention areprepared by reacting a polyisocyanate and a polyfunctionalisocyanate-reactive polymer under foam forming conditions to prepare arigid polyurethane foam and by crushing this rigid polyurethane foam.Further the present invention is concerned with the process forpreparing such rigid foams and with reaction systems comprising theingredients for making such foams.

In the context of the present invention the following terms have thefollowing meaning:

1) isocyanate index or NCO index or index:

the ratio of NCO-groups over isocyanate-reactive hydrogen atoms presentin a formulation, given as a percentage:$\frac{\lbrack{NCO}\rbrack \times 100}{\text{[active hydrogen]}}{(\%).}$

In other words the NCO-index expresses the percentage of isocyanateactually used in a formulation with respect to the amount of isocyanatetheoretically required for reacting with the amount ofisocyanate-reactive hydrogen used in a formulation.

It should be observed that the isocyanate index as used herein isconsidered from the point of view of the actual foaming processinvolving the isocyanate ingredient and the isocyanate-reactiveingredients. Any isocyanate groups consumed in a preliminary step toproduce modified polyisocyanates (including such isocyanate-derivativesreferred to in the art as quasi or semi-prepolymers and prepolymers) orany active hydrogens consumed in a preliminary step (e.g. reacted withisocyanate to produce modified polyols or polyamines) are not taken intoaccount in the calculation of the isocyanate index. Only the freeisocyanate groups and the free isocyanate-reactive hydrogens (includingthose of the water) present at the actual foaming stage are taken intoaccount.

2) The expression “isocyanate-reactive hydrogen atoms” as used hereinfor the purpose of calculating the isocyanate index refers to the totalof active hydrogen atoms in hydroxyl and amine groups present in thereactive compositions; this means that for the purpose of calculatingthe isocyanate index at the actual foaming process one hydroxyl group isconsidered to comprise one reactive hydrogen, one primary amine group isconsidered to comprise one reactive hydrogen and one water molecule isconsidered to comprise two active hydrogens.

3) Reaction system: a combination of components wherein thepolyisocyanates are kept in one or more containers separate from theisocyanate-reactive components.

4) The expression “polyurethane foam” as used herein refers to cellularproducts as obtained by reacting polyisocyanates withisocyanate-reactive hydrogen containing compounds, using foaming agents,and in particular includes cellular products obtained with water asreactive foaming agent (involving a reaction of water with isocyanategroups yielding urea linkages and carbon dioxide and producingpolyurea-urethane foams) and with polyols, aminoalcohols and/orpolyamines as isocyanate-reactive compounds.

5) The term “average nominal hydroxyl functionality” is used herein toindicate the number average functionality (number of hydroxyl groups permolecule) of the polyol or polyol composition on the assumption thatthis is the number average functionality (number of active hydrogenatoms per molecule) of the initiators) used in their preparationalthough in practice it will often be somewhat less because of someterminal unsaturation.

6) The word “average” refers to number average unless indicatedotherwise.

The foams according to the present invention are prepared by reacting apolyisocyanate (1), an isocyanate-reactive compound (2), said compound(2) having an average equivalent weight of at most 374 and an averagenumber of isocyanate-reactive hydrogen atoms of from 2 to 8, anisocyanate-reactive compound (3), said compound (3) iS having an averageequivalent weight of more than 374 and an average number ofisocyanate-reactive hydrogen atoms of from 2 to 6 and water to prepare arigid polyurethane foam and by crushing this rigid polyurethane foam.

Further the present invention is concerned with reaction systemscomprising the above ingredients. The present invention is alsoconcerned with a process for preparing rigid polyurethane foams usingthe above ingredients. More in particular the foams according to thepresent invention are prepared by reacting a polyisocyanate (1), apolyol (2) having a hydroxyl number of at least 150 mg KOH/g and anaverage nominal hydroxyl functionality of from 2 to 8, a polyol (3)having a hydroxyl number of from 10 to less than 150 mg KOH/g and anaverage nominal hydroxyl functionality of from 2 to 6 and water toprepare a rigid polyurethane foam and by crushing this rigidpolyurethane foam.

Suitable organic polyisocyanates for use in the process of the presentinvention include any of those known in the art for the preparation ofrigid polyurethane foams, like aliphatic, cycloaliphatic, araliphaticand, preferably, aromatic polyisocyanates, such as toluene diisocyanatein the form of its 2,4 and 2,6-isomers and mixtures thereof anddiphenylmethane diisocyanate in the form of its 2,4′-, 2,2′- and4,4′-isomers and mixtures thereof, the mixtures of diphenylmethanediisocyanates (MDI) and oligomers thereof having an isocyanatefunctionality greater than 2 known in the art as “crude” or polymericMDI (polymethylene polyphenylene polyisocyanates), the known variants ofMDI comprising urethane, allophanate, urea, biuret, carbodiimide,uretonimine and/or isocyanurate groups.

Isocyanate-reactive compounds (2) include any of those known in the artfor that purpose like polyamines, aminoalcohols and polyols. ofparticular importance for the preparation of the rigid foams are polyolsand polyol mixtures having hydroxyl numbers of at least 150 mg KOH/g andan average nominal hydroxyl functionality of from 2 to 6. Suitablepolyols have been fully described in the prior art and include reactionproducts of alkylene oxides, for example ethylene oxide and/or propyleneoxide, with initiators containing from 2 to 8 active hydrogen atoms permolecule. Suitable initiators include: polyols, for example ethyleneglycol, diethylene glycol, propylene glycol, dipropylene glycol, butanediol, glycerol, trimethylolpropane, triethanolamine, pentaerythritol,sorbitol and sucrose; polyamines, for example ethylene diamine, tolylenediamine, diaminodiphenylmethane and polymethylene polyphenylenepolyamines; and aminoalcohols, for example ethanolamine anddiethanolamine; and mixtures of such initiators. Other suitable polyolsinclude polyesters obtained by the condensation of appropriateproportions of glycols and higher functionality polyols withpolycarboxylic acids. Still further suitable polyols include hydroxylterminated polythioethers, polyamides, polyesteramides, polycarbonates,polyacetals, polyolefins and polysiloxanes. Still further suitableisocyanate-reactive compounds include ethylene glycol, diethyleneglycol, propylene glycol, dipropylene glycol, butane diol, glycerol,trimethylolpropane, ethylene diamine, ethanolamine, diethanolamine,triethanolamine and the other initiators mentioned before. Mixtures ofsuch isocyanate-reactive compounds may be used as well.

Isocyanate-reactive compounds (3) include any of those known in the artfor that purpose, like polyamines, aminoalcohols and polyols. ofparticular importance for the preparation of the rigid foams are polyolsand polyol mixtures having a hydroxyl value of 10 to less than 150 andpreferably of 15-60 mg KOH/g and an average nominal hydroxylfunctionality of from 2 to 6 and preferably of from 2 to 4. These highmolecular weight polyols are generally known in the art and includereaction products of alkylene oxides, for example ethylene oxide and/orpropylene oxide, with initiators containing from 2 to 6 active hydrogenatoms per molecule. Suitable initiators include: polyols, for exampleethylene glycol, diethylene glycol, propylene glycol, dipropyleneglycol, butane diol, glycerol, trimethylolpropane, triethanolamine,pentaerythritol and sorbitol; polyamines, for example ethylene diamine,tolylene diamine, diaminodiphenylmethane and polymethylene polyphenylenepolyamines; and aminoalcohols, for example ethanolamine anddiethanolamine; and mixtures of such initiators. Other suitable polyolsinclude polyesters obtained by the condensation of appropriateproportions of glycols and higher functionality polyols withpolycarboxylic acids. Still further suitable polyols include hydroxylterminated polythioethers, polyamides, polyesteramides, polycarbonates,polyacetals, polyolefins and polysiloxanes. Preferred polyols are thepolyether polyols comprising ethylene oxide and/or propylene oxide unitsand most preferably polyoxyethylene polyoxypropylene polyols having anoxyethylene content of at least 20% by weight. Other polyols which maybe used comprise dispersions or solutions of addition or condensationpolymers in polyols of the types described above. Such modified polyols,often referred to as “polymer” polyols have been fully described in theprior art and include products obtained by the in situ polymerisation ofone or more vinyl monomers, for example styrene and acrylonitrile, inpolymeric polyols, for example polyether polyols, or by the in situreaction between a polyisocyanate and an amino- or hydroxy-functionalcompound, such as triethanolamine, in a polymeric polyol.

The polymer modified polyols which are particularly interesting inaccordance with the invention are products obtained by in situpolymerisation of styrene and/or acrylonitrile inpoly(oxyethylene/oxypropylene) polyols and products obtained by in situreaction between a polyisocyanate and an amino or hydroxy-functionalcompound (such as triethanolamine) in a poly(oxyethylene/oxypropylene)polyol. Polyoxyalkylene polyols containing from 5 to 50% of dispersedpolymer are particularly useful. Particle sizes of the dispersed polymerof less than 50 microns are preferred. Mixtures of suchisocyanate-reactive compounds may be used as well.

The relative amount of isocyanate-reactive compound (2) and (3) orpolyol (2) and (3) may vary widely and preferably ranges from 0.1:1 to4:1 (w:w).

The relative quantities of the polyisocyanate and theisocyanate-reactive compounds to be reacted may vary within a widerange. In general an isocyanate index will be applied of from 25 to 300,preferably of from 30 to 200 and most preferably of from 40 to 150.

In order to prepare a foam water is used as a blowing agent. However ifthe amount of water is not sufficient to obtain the desired density ofthe foam any other known way to prepare polyurethane foams may beemployed additionally, like the use of reduced or variable pressure, theuse of a gas like air, N₂ and CO₂, the use of more conventional blowingagents like chlorofluorocarbons, hydrofluorocarbons, hydrocarbons andfluorocarbons, the use of other reactive blowing agents, i.e. agentswhich react with any of the ingredients in the reacting mixture and dueto this reaction liberate a gas which causes the mixture to foam and theuse of catalysts which enhance a reaction which leads to gas formationlike the use of carbodiimide-formation-enhancing catalysts such asphospholene oxides. Combinations of these ways to make foams may be usedas well. The amount of blowing agent may vary widely and primarilydepends on the desired density. Water may be used as liquid atbelow-ambient, ambient or elevated temperature and as steam.

Per 100 parts by weight of polyisocyanate (1), isocyanate-reactivecompound (2) and compound (3) or polyol (2) and polyol (3) and water,preferably the amount of compound (2) or polyol (2) ranges from 2-20parts by weight, the amount of compound (3) or polyol (3) ranges from5-35 parts by weight and the amount of water ranges from 1 to 17 partsby weight, the remainder being polyisocyanate. This encompasses anotheraspect of the invention: if a cyclic polyisocyanate and more inparticular an aromatic polyisocyanate and most in particular an MDI orpolymethylene polyphenylene polyisocyanate is used the content of cyclicand more in particular of aromatic residues in the flexible foam isrelatively high as compared to conventional flexible polyurethane foams.The foams according to the invention preferably have a content ofbenzene rings, derived from aromatic polyisocyanates, which is 30 to 56and most preferably 35 to 50% by weight based on the weight of the foam.since polyols, polymer polyols, fire retardants, chain extenders and/orfillers which contain benzene rings may be used, the overall benzenering content of the flexible foam may be higher and preferably rangesfrom 30 to 70 and most preferably from 35 to 65% weight as measured bycalibrated Fourier Transform Infra Red Analysis.

In addition to the polyisocyanate, the isocyanate-reactive compounds andthe blowing agent, one or more auxiliaries or additives known per se forthe production of polyurethane foams may be used. Such optionalauxiliaries or additives include foam-stabilizing agents or surfactants,for example siloxane-oxyalkylene copolymers and polyoxyethylenepolyoxypropylene block copolymers, urethane/urea catalysts, for exampletin compounds such as stannous octoate or dibutyltin dilaurate and/ortertiary amines such as dimethylcyclohexylamine or triethylene diamineand/or phosphates like NaH₂PO₄ and Na₂HPO₄, and fire retardants, forexample halogenated alkyl phosphates such as tris chloropropylphosphate, melamine and guanidine carbonate, anti-oxidants, UVstabilisers, anti-microbial and anti-fungal compounds and fillers likelatex, TPU, silicates, barium and calcium sulphates, chalk, glass fibersor beads and polyurethane waste material.

In operating the process for making rigid foams according to theinvention, the known one-shot, prepolymer or semi-prepolymer techniquesmay be used together with conventional mixing methods and the rigid foammay be produced in the form of slabstock, mouldings including foam infabric and pour-in-place applications, sprayed foam, frothed foam orlaminates with other materials such as hardboard, plasterboard,plastics, paper or metal or with other foam layers.

It is convenient in many applications to provide the components forpolyurethane production in pre-blended formulations based on each of theprimary polyisocyanate and isocyanate-reactive components. Inparticular, an isocyanate-reactive composition may be used whichcontains the auxiliaries, additives and the blowing agent in addition tothe isocyanate-reactive compounds (2) and (3) in the form of a solution,an emulsion or dispersion.

The rigid foam is prepared by allowing the aforementioned ingredients toreact and foam until the foam does not rise any more. Subsequently thefoam may be crushed. It is however preferred to allow the rigid foamobtained to cool down to below 80° C., preferably below 50° C. and mostpreferably to ambient temperature prior to crushing. After rise curingof the foam may be continued as long as desirable. In general a curingperiod of 1 minute to 24 hours and preferably of 5 minutes to 12 hourswill be sufficient. If desired curing may be conducted at elevatedtemperature. The rigid foam (i.e. before crushing) preferably has adensity of 3-27 and most preferably of 3-18 kg/m³.

The rigid foam (i.e. before crushing) prepared has a substantial amountof open cells. Preferably the cells of the rigid foam are predominantlyopen.

The crushing may be conducted in any known manner and by any knownmeans. The crushing may for instance be conducted by applying mechanicalforce onto the foam by means of a flat or pre-shaped surface or byapplying variations of external pressure.

In most cases a mechanical force sufficient to decrease the dimension ofthe foam in the direction of the crushing by 1-90%, preferably by 50-90%will be appropriate. If desired crushing may be repeated and/or carriedout in different directions of the foam. Due to the crushing the ballrebound increases considerably in the direction of the crushing. Due tothe crushing the density of the foam may increase. In general thisincrease will not exceed 30% of the density before crushing.

Although it is difficult to give more precise directions for thecrushing since it will inter alia depend on the density of the foam, therigidity of the foam, the type of crushing device used, we believe thoseskilled in the art are sufficiently aware of the phenomenon of crushingof polyurethane foams that they will be able to determine theappropriate crushing manner and means with the above guidance, certainlyin the light of the following examples.

After the crushing a novel flexible foam is obtained which hasexceptional properties. Despite the fact that the foam is flexible, itdoes not show a significant change of the Young's storage modulus E′over a temperature range from −100° C. to +25° C., as described before.The foam shows even in the absence of flame retardant additives goodfire retardant properties. The oxygen index of the foam prepared fromaromatic polyisocyanates preferably is above 20 (ASTM 2863); Further itshows a Young's storage modulus at 25° C. of at most 500 kPa, preferablyat most 350 kPa, most preferably between 10-200 kPa and a sag factor(CLD 65/25, ISO 3386/1) of at least 2.0, preferably at least 3.5 andmost preferably of 4.5-10. CLD hysteresis loss values for the foams arebelow 55% and preferably below 50% (which is calculated by the formula${\frac{\left( {A - B} \right)}{A} \times 100\%},$

wherein A and B stand for the area under the stress/strain curve of theloading (A) and unloading (B) as measured according to ISO 3386/1).Still further these foams can be manufactured with a very low or evennegative Poisson's ratio as determined by lateral extension studiesunder compression of the foams. Finally compression set values of thefoams are generally low, preferably below 40% (ISO 1856 Method A, normalprocedure).

If the Tg^(h) is not too high the foam might be used in thermoformingprocesses to prepare shaped articles. Preferably the Tg^(h) of the foamis between 80 and 180° C., most preferably between 80° C. and 160° C.for such thermoforming applications.

Further the foams show good load-bearing properties like compressionhardness values without the use of external fillers together with a goodresilience, tear strength and durability (fatigue resistance) even atvery low densities. In conventional flexible foams often high amounts offiller need to be used to obtain satisfactory load-bearing properties.Such high amounts of fillers hamper the processing due to a viscosityincrease.

The foams of the present invention may be used as cushioning material infurniture and automotive seating and in mattresses, as carpet backing,as hydrophilic foam in diapers, as packaging foam, as foams for soundinsulation in automotive applications and for vibration isolation ingeneral.

The invention is illustrated by the following examples.

EXAMPLE 1

A polyisocyanate mixture was prepared by mixing 56.6 parts by weight ofpolymeric MDI having an NCO value of 30.7% by weight and an isocyanatefunctionality of 2.7 and 43.4 parts by weight of a uretonimine modifiedMDI having an NCO value of 31% by weight, an isocyanate functionality of2.09, a uretonimine content of 17% by eight and 2,4′-MDI content of 20%by weight.

An isocyanate-reactive composition was prepared by mixing 32.2 arts byweight (pbw) of polyethylene glycol having a molecular weight of 200,4.5 pbw of ethylene glycol, 42.6 pbw of an EO/PO polyol having a nominalfunctionality of 2, an EO content of 20.2% by weight (all tipped) andhydroxyl value of 30 mg KOH/g, 5.5 pbw of diethanolamine, 14.5 pbw ofwater and 0.7 pbw of di-butyl-tin-dilaurate. This composition was anemulsion.

106.1 pbw of the polyisocyanate mixture and 46.9 pbw of theisocyanate-reactive composition (isocyanate index 75.5) were mixed for13 seconds using a Heidolph™ mechanical mixer at a speed of 5000 roundsper minute (rpm). After mixing the reaction mixture was poured in anopen 5 liter bucket and allowed to react. Prior to the pouring of thereaction mixture into the bucket, the inner walls of the bucket weregreased with release agent Desmotrol™ D-10RT. 2½ minutes after the foamhas stopped rising (foam rise time 70 seconds) the foam was taken out ofthe bucket and allowed to cool to ambient temperature. A rigidpolyurethane foam was obtained. Core foam samples were then cut out ofthe centre of the foam for property evaluation. The free rise coredensity was 11 kg/m³ (ISO/DIS845). Then the samples were crushed by onecompression (70% CLD) in the rise direction of the foam using anInstron™ mechanical tester mounted with flat plates.

After crushing a flexible foam was obtained having no major glass-rubbertransition between −100° C. and +25° C. and having the followingproperties :

free rise core density (ISO/DIS 845, kg/m³) 13 ball rebound (ISO8307,%), measured in the direction 59 of crushing tensile strength at break(ISO-1798, kpa) 71 elongation at break (ISO-1798, %) 30 tear strength(ISO/DIS 8067, N/m) 70 compression set (ISO 1856, method A, %) 38 CLD−25% (ISO 3386/1, kpa) 3.2 CLD = compression load deflection) CLD −40%(ISO 3386/1, kpa) 5.2 CLD −65% (ISO 3386/1, kpa) 18.3 CLD sag factor(ISO 3386/1) 5.7 CLD hysteresis loss (ISO 3386/1, %) 48 tan δ_(max)(−100° C. to +25° C.) (ISO/DIS 6721-5) 0.06 oxygen index (ASTM 2863, %)20.5${{Young}’}s\quad {storage}\quad {modulus}\quad {ratio}\quad \frac{E^{\prime} - {100{^\circ}\quad {C.}}}{E^{\prime} + {25{^\circ}\quad {C.}}}\quad \text{(}{ISO}\text{/}{DIS}\quad 6721\text{-}5\text{)}$

2.0 Young's storage modulus at 25° C. (ISO/DIS 6721-5, kpa) 180 Benzenecontent, % by weight (calculated) 43.5

Compression foam properties were measured in the rise/crushing directionof the foam.

DMTA-test

Measurements were carried out according to ISO/DIS 6721-5 on aRheometric Scientific DMTA apparatus using a 3-point bending mode.Sample test dimensions were: length 1.0 cm, width 1.3 cm, thickness 0.4cm. Applied strain amplitude 64×10⁻⁴ cm, frequency 1 Hz, heating rate 3°C./min. The foam samples were pre-conditioned at 23° C./50% RH for 24hours prior testing. The foam samples were quenched to −120° C. (coolingrate 8.5° C./min) and held at that temperature for 5 minutes beforeheating of the sample was started.

EXAMPLE 2

Three isocyanate reactive blends (blend A, B and C) were prepared. BlendA was prepared by mixing 200 pbw of the EO/PO polyol of example 1 and6.5 pbw of ‘DABCO’ T9 (catalyst from AIR PRODUCTS, DABCO is a trademark). Blend B was prepared by mixing 75.5 pbw of polyethylene glycolwith a molecular weight of 200 and 5.56 pbw of ‘IRGANOX’ 5057 ( ananti-oxydant from Ciba-Geigy Ltd., IRGANOX is a trademark). Blend C wasprepared by mixing 23.5 pbw of triethylene glycol, 40.0 pbw of water and0.6 pbw of monobasic sodium phosphate.

166.1 pbw of blend A, 65.2 pbw of blend B, 51.6 pbw of blend C and 617.1pbw of the isocyanate blend of example 1 (isocyanate index 100) weremixed for 13 seconds using an ‘Ytron’ (trademark) mechanical mixer at aspeed of 3500 rpm. After mixing the reaction mixture was poured in anopen 50×50×30 cm³ wooden mould. Prior to pouring the mixture in thewooden mould, the inner walls were covered with paper. One hour afterthe foam had stopped rising (foam rise time 70 seconds) the foam wastaken out of the mould and allowed to cool to ambient temperature. Thefoam was cut and crushed as in example 1. The free rise core densitybefore crushing was 13 kg/m³.

After crushing a flexible foam was obtained having no major glass-rubbertransition between −100° C. and +25° C. and having the followingproperties (test procedures as in example 1):

free rise core density (kg/m³) 15 ball rebound (%) 62 tensile strengthat break (kPa) 67 elongation at break (%) 49 compression set (%) 31CLD-40% 7.1 Young's storage modulus ratio (E′ −100° C./E′ +25° C.) 2.8Young's storage modulus (kPa) 158 benzene content, % by weightcalculated 42.6

EXAMPLE 3

Two isocyanate reactive blends (blend A and B) were prepared. Blend Awas prepared by mixing 30 pbw of the EO/PO polyol of example 1, 0.3 pbwof ‘DABOO’ T9 and 0.3 pbw of 1-methyl-1-oxo-phospholene (a carbodiimidecatalyst from Hoechst). Blend B was prepared by mixing 11.3 pbw ofpolyethylene glycol with a molecular weight of 200, 1.95 pbw ofdiethanolamine, 1.58 pbw of ethylene glycol and 4.5 pbw of water.

26.9 pbw of blend A, 17.3 pbw of blend B and 108.6 pbw of the isocyanateblend of example 1 (isocyanate index 123) were mixed for 13 seconds witha ‘Heidolph’ mechanical mixer at a speed of 5000 rpm. After mixing thereaction mixture was poured in an open 5 liter bucket and allowed toreact. One hour after the foam has stopped rising (foam rise time 70seconds) the foam was taken out of the bucket and allowed to cool toambient temperature. A rigid polyurethane foam was obtained with a freerise density of 16 kg/m³. Attenuated total reflection Fourier transforminfra red analysis showed the presence of carbodiimide groups (signal at2140 cm⁻¹).

After crushing as described in example 1 a flexible foam having no majorglass-rubber transition between −100° C. and +25° C. was obtained withthe following mechanical properties (test procedures as in example 1):

free rise core density (kg/m³) 18 ball rebound (%) 48 Young's storagemodulus ratio (E′ −100° C./E′ +25° C.) 2.5 Young's storage modulus at25° C. (kPa) 126 benzene content, % by weight calculated 42.9

What is claimed is:
 1. A process for preparing a rigid polyurethane foamby reacting: (1) a polyisocyanate; (2) an isocyanate reactive compoundhaving an average equivalent weight of at most 374 and an average numberof isocyanate-reactive hydrogen atoms of from 2 to 8; (3) anisocyanate-reactive compound having an average equivalent weight of morethan 374 and an average number of isocyanate-reactive hydrogen atoms offrom 2 to 6; and (4) water, wherein a total weight of compound (1),compound (2), compound (3) and compound (4) represents 100 parts perweight, the amount of compound (2) ranges from 2-20 parts by weightrelative to the total weight, the amount of compound (3) ranges from5-35 parts by weight relative to the total weight and the amount ofcompound (4) ranges from 1-17 parts by weight relative to the totalweight.
 2. A Process for preparing a rigid polyurethane foam byreacting: (1) a polyisocyanate; (2) a polyol having a hydroxyl number ofat least 150 mg KOH/g and average nominal hydroxyl functionality of from2 to 8; (3) a polyol having a hydroxyl number from 10 to less than 150and average nominal hydroxyl functionality of from 2 to 8; and (4)water, wherein a total weight of compound (1), compound (2), compound(3) and compound (4) represents 100 parts per weight, the amount ofcompound (2) ranges from 2-20 parts by weight relative to the totalweight, the amount of compound (3) ranges from 5-35 parts by weightrelative to the total weight and the amount of compound (4) ranges from1-17 parts by weight relative to the total weight.
 3. The Process forpreparing a rigid polyurethane foam as recited in claim 1, wherein theweight ratio of compound (2): compound (3) is 0.1 to 4:1.
 4. The Processfor preparing a rigid polyurethane foam as recited in claim 2, whereinthe weight ratio of compound (2): compound (3) is 0.1 to 4:1.